First let me say that forwarding is a bad idea and will only get worse as SPF and other spam prevention techniques get more popular. SPF is generally broken when you use forwarding. SRS (Sender Rewriting Scheme) can in some cases make SPF work by itself, but the result does not allow proper DMARC alignment. If you own a domain, it's far superior for your domain DNS records to point to the final destination server where you read your mail, not a forwarding service.

As I understand your situation, you own a domain and are attempting to deliver incoming email to a forwarding service. The forwarding service will then forward the message to your live.co.uk account where you read your mail. Is that correct?

For this to work:

Your own domain must have proper MX records pointing to the incoming mail server at the forwarding service. It's recommended that they supply at least two IP addresses.

The forwarding service must be configured to accept messages sent to your domain.

From the error message you posted, either your domain's MX records are pointing to the wrong mail server, or the forwarding server is not configured to accept mail for your domain.

You can test your domain email records as follows. Go to:http://mxtoolbox.com/DNSLookup.aspx
Enter your domain name and click DNS Lookup. On the next page, click the MX Lookup link. You should then see the MX mail delivery servers for your domain. Ideally there are at least two shown. The nameserver IP addresses should match what the forwarding service specifies for your use.

Now click on the first SMTP Test link (for the first MX entry). After a few seconds you should see the results of several tests. Ideally all tests should pass (green). If the first one shows a slow connection time warning, click the Test Email Server button to try it again (caching may improve the response time on the second try).

If some of these tests fail it may be due to the DNS records for your domain not being set up correctly. This has nothing to do at this stage with SPF. I'm talking about your DNS records not pointing to the correct incoming mail server. Each DNS entry has a TTL (Time To Live) value. The TTL value shows how long the old data should be cached in the DNS system at various locations. So if you make any changes to a DNS entry, after saving your changes you must wait a little longer than the TTL time before you are guaranteed that these changes are visible to Internet users. So if you have a very long TTL set now, you won't be able to make any changes which have an effect until the TTL delay. So if you plan to change any DNS entries, you should change the TTL on the entries you plan to change as soon as possible to a small value (such as 1 minute or 60 seconds). You then have to wait for the previously set old TTL interval. Then you can make changes and they will take place in only 1 minute.

If these tests all pass (and the MX host names look good and the IP values are what your forwarding service specifies), then the forwarding MX incoming mail server isn't accepting mail for your domain. Check your account to see if you are paid up and your configuration is correct.